The present invention relates to a method and apparatus for ink jet printing on a gelatin coated media. More particularly, the present invention relates to a method and apparatus for heating the gelatin coated media to control absorption of ink into a gelatin surface layer of the media.
Ink jet printers operate by expelling ink from a plurality of nozzles. In the case of thermal ink jet printers one or more resistors are associated with each of the plurality of nozzles. The resistors when energized vaporize ink to produce a rapidly expanding bubble to expel a selected volume of ink from a selected nozzle toward the print media.
The nozzles, resistors and ink together form a print cartridge. The print cartridge is moved relative to the print media as ink is expelled from the nozzles to form images on the media. Frequently, the print cartridge is mounted in a print carriage that is moved or scanned repeatedly across the print media width as the print media is advanced to form the output image.
In the case of color printing, the print cartridge contains more than one color ink. In the case of four color printing the print cartridge usually contains cyan, magenta, yellow and black inks. Each of the colored inks within the print cartridge have associated nozzles. By selectively energizing resistors as the print cartridge is moved across the media color images are formed on the print media.
The accuracy and consistency in which the printer delivers ink droplets to the print media as well as the interaction of the ink with the media effects the output image visual quality. The printers ability to deliver droplets of ink is generally related to the printer resolution. The resolution of a printer is related to the size of an individual picture element formed by each individual droplet of ink as well as the printers ability to correctly position each of these individual picture elements on the media surface.
In addition, attempts have been made to improve the output image quality by improvements to the interaction of the ink with the output media. Problems that are associated with the interaction of ink with the media include ink bleed, ink coalescence on the media surface, and cockling or warping of the media resulting from ink saturation. The ink used in thermal ink jet printing is an aqueous ink having a liquid base. When the liquid ink is deposited on wood based papers, it absorbs into the cellulose fibers and causes the fibers to swell. As the cellulose fibers swell, they generate localized expansions, which in turn, causes the paper to warp uncontrollably in these regions. This phenomena called paper cockle can cause a degradation of print quality due to uncontrolled orifice to media spacing, and can cause the printed output to have a low quality appearance due to the wrinkled paper.
One solution that has been used to eliminate or reduce cockling has been to dry the ink rapidly after it is printed. High output heaters are usually required to accelerate the ink drying process. There are several problems associated with using high output heaters to accelerate ink drying. Too much heat can cause polyester media to wrinkle and cellulose based media to turn yellow. In addition, excess heat can overheat the print cartridges, resulting in larger drops of ink being expelled during print operations thereby increasing the cost per copy. If the print cartridges become too hot, the cartridges will stop working. Excessive heat within the printer housing can cause melting and deforming of plastic components and shorten the life of electronic components.
The use of high output heaters in printers has sometimes produced additional problems such as buckling problems that can require the additional techniques such as the use of pre-heaters for drying the print medium under high humidity conditions. These pre-heaters have been used to dry the medium before reaching the print zone to prevent uneven shrinkage of the medium which can occur if not pre-heated. Uneven shrinkage of the medium results because of the localized nature of the high output heating which produces uneven heating which can cause buckling of the medium. Buckling of the print medium produces uneven spacing between the medium and print orifices which can effect the output image quality. In extreme cases if the output medium contacts the print orifices smearing can result.
As mentioned previously, the use of high output heaters can produce additional problems such as excessive heat within the printer housing. To prevent excessive overheating of the print nozzles resulting from the high output heaters one or more fans have been used for cooling. The use of cooling fans in printers having output heaters adds to the cost of the printer as well as the size and weight, and manufacturability which is undesirable.
There is a present need for relatively low cost printers that are capable of providing high quality output images. These printers should minimize ink running on the media surface as well as minimize ink bleed. In addition, the output images should have relatively fast dry times.